System of electrostatic quadrupole micro-lenses

ABSTRACT

The system comprises an array of parallel filiform electrodes and each micro-lens is made up of at least four adjacent electrodes which define a tunnel having a cross-section in the shape of a square. Each vertex of the square is intercepted by a quarter-circle of the cross-section of the adjacent one of said electrodes and the cross-section of said array in a plane at right angles to said electrodes forms a substantially square lattice. Means are also provided for electrically polarizing said electrodes.

United States Patent 1 1 Guernet [451 Feb. 20, 1973 s41 SYSTEM OFELECTROSTATIC 3,497,744 2 1970 Himmelbauer et a1. .313/78 QUADRUPOLEMICRO-LENSES 3,612,946 10 1971 Toyoda ..313 103 x [75] Inventor: GeorgesGuernet, Grenoble, France OTHER PUBLICATIONS 1 1 Assignee:com'lfissariat A LEmrgie IEE Transactions on Microwave Theory &Techniques 's Pam, France vol. MTT-l4, No. 12 Dec. 1966 pp. 657665 [22]Filed: Jan. 19, 1971 350-175GN A Light Beam Waveguide UsingHyperbolic-Type Gas Lenses by Suematsu et a1. [21] Appl. No.: 107,720

Primary ExaminerNathan Kaufman 30 Foreign Application Priority DataAttorney-Cameron, Kerkam & S n

Jan. 20, 1970 France ..7001862 [57] ABSTRACT [52] U.S. C1. ..3l3/23l,313/78, 313/63, The system comprises an array of parallel filiform /495electrodes and each micro-lens is made up of at least [51] Int. Cl...H01j 17/26, Holj 61/28 four adjacent electrodes which define a tunnelhaving 1 Field of Search a cross-section in the shape of a square. Eachvertex 313/75, 105! 107-5, 103; M C, of the square is intercepted by aquarter-circle of the DS; 330/4-7 cross-section of the adjacent one ofsaid electrodes and the cross-section of said array in a plane at right[56] References Cted angles to said electrodes forms a substantiallysquare UNITED STATES PATENTS lattice. Means are also provided forelectrically polarizing said electrodes. 2,919,381 12/1959 Glaser..250/49.5 C X 2,941,114 6/1960 Cook ..3l3/83 X 11 Claims, 4 DrawingFigures M/C/PO-BEA/ s f [LECTF/CAILY INSULATING MATERIAL i PRINTEDC/kCU/T INSULATING MATfR/AL MEANS TO POLARIZE THE ELECTRODES 1 ELECTRICCONNECTIONS RINTED CIRCUITS \DC VOLTAGE SOURCE v CIRCUITS PmEmEnFwaoms3,717, 785

SHEET 2 BF 3 I B MEANS TO POLARIZE THE ELECTRODES 1 ELECTRIC CONNE OFPRINTED v ELEC c CONNE 0 OF PRINTED CIRCUITS lllli PATENTEDFEBZOQH 5717.7 85 sum 3 or 3 SYSTEM OF ELECTROSTATIC QUADRUPOLE MICRO-LENSES Thisinvention is concerned with a system of electrostatic quadrupolemicro-lenses, that is to say an assembly of electrostatic lenses of verysmall size, each lens being made up of four electric poles. This systemmakes it possible to obtain at the same time from a beam of electricallycharged particles of large crosssectional area a plurality ofmicro-beams of small crosssectional area which are parallel to eachother and convergent.

Quadrupole lenses are employed for the purpose of focusing a beam ofcharged particles and said particles can be either ions or electrons.Modification of the charged-particle paths is obtained by means of fourelectrodes which are usually placed symmetrically with respect to theaxis of the incident beam. These electrodes are metallic and usuallyhave a hyperbolic shape. Said electrodes are polarized by applyingthereto an electric voltage having a value which depends on the natureand velocity of the particles as well as on the angle of convergence tobe given to the particle beam. In some applications such as ionimplantation of charged particles in semiconductor material, it is ofinterest to have available at the same time micro-beams of smallcross-sectional area which are parallel to each other and focused, thedistance between two adjacent microbeams being very small (a fewmillimeters, for example). The design concept of electrostatic lenses ofthe prior art is such that the electrodes are usually of large size. Inorder to obtain simultaneously a plurality of micro-beams from a beam ofincident particles of substantial cross-sectional area, it would benecessary in the case of known devices to produce an incident beamhaving a much larger cross-sectional area than any beam which can beproduced in the present state of knowledge. Moreover, the spacingbetween two microbeams would be relatively substantial.

The invention provides a device which meets practical requirements moreeffectively than any comparable devices of the prior art, particularlyinsofar as the disadvantages mentioned above no longer arise. Theinvention is primarily intended to provide a system of electrostaticquadrupole lenses which deliver from an incident beam of substantialcross-sectional area focused micro-beams which are parallel to eachother and such that the distance between two adjacent microbeams is verysmall.

More specifically, the invention proposes a system of electrostaticquadrupole micro-lenses which essentially comprises an array of parallelfiliform electrodes, each microlens being made up of at least fouradjacent electrodes which delimit a tunnel having a cross-sectionsubstantially in the shape of a square which is truncated at each vertexby a quarter-circle of the cross-section of the one of said electrodesand the cross-section of said array in a plane at right angles to saidelectrodes being such as to form a substantially square lattice, andmeans for electrically polarizing said electrodes.

in a first embodiment, said system is such that each of said tunnels isdelimited by four adjacent electrodes each constituted at the surface bytwo electrically conducting portions separated by an electricallyinsulating portion.

In a second embodiment, said system is such that each micro-lens isconstituted by two groups each formed by four adjacent electrodes, eachelectrode of one of said two groups being located in the line ofextension of an electrode of the other group.

A better understanding of the invention will be obtained byconsideration of the following description of two modes of execution ofthe invention which are given by way of non-[imitative example,reference being made in the description to the accompanying drawings, inwhich FIG. 1 illustrates a first embodiment of the invention FIG. 2illustrates a cross-section of the device taken in the direction of thearrow A of FIG. 1

FIG. 3 is a detail view of a micro-lens;

FIG. 4 is a partial view of the second embodiment.

The device which is illustrated in FIG. ll comprises a set of filiformelectrodes 1 and three plates 2, 3 and 4 having flat parallel faces, theplates 2 and 3 being in juxtaposed relation. The ends of each electrodeare inserted in cylindrical holes 5 and 6 which serve as recesses andare pierced in oppositely-facing relation in the plates 3 and 4respectively. The filiform electrodes 1 which are at right angles to theplates 2, 3 and 4 are formed of electrically insulating material. Theholes 5 and 6 form a square lattice on eachplate 3 and 4. Bores 7 and 8are pierced from one side to the other and parallel to the electrodes 1in the plates 2, 3 and 4 respectively at an equal distance from theholes 5 and 6. Said bores are therefore located along the same axiswhich is parallel to the electrodes 1 and therefore form a squarelattice in the plates 2, 3 and 4. The bores 7 have the shape of twocylinders which are joined to each other by a cone frustum and one ofwhich therefore has a much smaller diameter than the other. The bores '7have a very small cross-sectional area at that end which is locatednearest the electrodes and within the plate 3. That portion of each bore7 which is located within the plate 2 has the same diameter as the bores8 of the plate 4. Two bores 7 and 8 in oppositelyfacing relation and thefour electrodes 1 which surround said two bores form a tunnel 9. A thinfilm 10 has been deposited at the surface and over a given length ateach end of the electrodes 1 each electrode 1 is therefore constitutedat the surface by two electrically conducting portions 10 separated byan electrically insulating portion 1 1.

Means illustrated in FIG. I serve to polarize the electrodes I. By wayof example, said means can consist of a printed circuit formed by a filmof electrically insulating material deposited on the opposite faces ofthe plates 3 and 4 of the electrodes 1 and by a metallic film which isdeposited selectively on the electrically insulating layer. Theconstruction of printed circuits of this type is known per se threesuccessive layers are deposited on the two faces of the plates 3 and 4which are located opposite to the electrodes the first layer is formedof electrically insulating material, the second layer is formed ofelectrically conducting material and the third layer is formed ofphotosensitive resin which is exposed through a screen representing thepattern of electric connections. The exposed resin is first removed bychemical etching and this is followed by removal of the metallic portionwhich is located beneath the exposed resin. Finally, the entire resinlayer is completely dissolved.

In FIG. 2 which shows a cross-section of the device of FIG. 1 as takenin the direction'of the arrow A, it is observed that the electrodes 1which are surrounded by their conductive layers as well as the tunnels 9form a square lattice. Each tunnel is delimited by four identicalelectrodes which are positioned symmetrically with respect to the axisof said tunnel.

In FIG. 3, there are shown in perspective four adjacent electrodes whichdelimit a tunnel 9 and form a micro-lens. The electrodes are polarizedas follows electricvoltages of equal value but of opposite sign areapplied to the electrically conducting portions designated by thereference numerals l2 and 13 in FIG. 3 (for example V in the case of theportion 12 and V in the case of the portion 13). The quarter circle ateach vertex of the square is shown in broken line.

The operation of the device is accordingly as follows the electricallycharged particles enter the device in the direction of the arrows 14 ofFIG.v l. The incident beam is then split up by the bores 7 which formcharged-particle beams of very small cross-sectional area. Said beamsare then focused as they pass through the tunnels 9. In the firstportion of the tunnel, the initially circular cross-section of themicro-beams becomes elliptic and then again becomes circular but smallerin the second portion. The micro-beams which emerge from the bores 8 arethen focused and have a very small cross-sectional area. By virtue ofthe system of micro-lenses formed by the electrodes 1, it is thereforepossible to form a set of focused micro-beams from an incident beam ofcharged particles having a large cross-sectional area by making use of adevice in accordance with the invention. In the case of identicalcharged particles having a given energy, the focal length of the lensesdepends on the value of the electric voltage which is applied to theelectrodes. The distance between two adjacent micro-beams is thedistance between two adjacent bores 8.

The plates 2, 3 and 4 are indium or nickel plates having thicknessesrespectively of 5 mm, 1.5 mm and 5 mm. The large diameter of the bores 7is equal to 1 mm whereas the small diameter is only 200 microns. Thebores 8 have a uniform diameter of 1 mm. The crosssection of fouradjacent electrodes which define a tunnel and constitute a micro-lensforms a square lattice, the length of each side being equal to 2 mm. Theelectrodes are formed of alumina wires each having a length of 25 mm anda diameter of 1 mm. The metallic coatings formed at each end of theelectrodes have a thickness of-lOOmicrons and are deposited over adistance of, 6 mm in the case of the portion which is located nearestthe plate 3 and over a distance of 8 mm in the case of the other portionwhich is located nearest the plate 4;

However, in the first embodiment of the system of micro-lenses, thelenses are formed .of electrodes having an electrically insulatingcentral portion, with the result that the distribution of the lines ofelectric force is not perfect. By improving this distribution, betterfocusing of the micro-beams can be obtained. Moreover, the electricallyinsulating portion of an electrode which is located between twoelectrically conducting portions stores charged particles during thecourse of time and becomes less and less insulating, with the resultthat the electric insulation between the two conducting portionsdeteriorates to a progressively greater extent. It then becomesnecessary to dismantle the system of micro-lenses in order to perform acleaning operation.

The present invention proposes a second vform of construction of thesystem of micro-lenses which is mechanically of more simple design andmakes it possible to obtain better focusing of the micro-beams.

In the second embodiment which is illustrated in FIG. 4, the systemcomprises three flat parallel plates 20, 22 and 24 having substantiallyparallel faces and of circular shape. Cylindrical bores 26 extendthrough the first plate 20 and are disposed on a square lattice. Theaxes 28 of said cylindrical bores are perpendicular to the plate 20.Cylindrical bores 30 and 32 extend through the plates 22 and 24respectively and are located in alignment with said axes 28. Thediameter of each cylindrical bore 30 and 32 is preferably verysubstantially smaller than the diameter of each bore 26. The bores 30and 32 form a square lattice which is identical with the lattice formedby the bores 26 in the plate 20 and have axes which are perpendicular tothe plates 22 and 24. Recesses which are disposed on a square latticeare pierced at right angles to the plates 22 and 24 around each bore 30and 32. An electrode 34 of cylindrical shape is fixed within eachrecess. SAid electrodes are located at the four corners of squares, thecenters of which correspond to the axis 28 of the bores 26, 30 and 32.The electrodes 34 of the plates 22 and 24 are placed in oppositerelation. This arrangement constitutes the most important part of themechanical portion of a system of quadrupole microlenses which isconstituted by an array of parallel filiform electrodes, each micro-lensbeing made up of two groups each formed of four adjacent electrodes. Forexample, a first group can comprise the electrodes 36, 38, 40 and 42 andthe second group corresponding to the first can comprise the electrodes44, 46, 48 and 50. Each electrode of one of these two groups is locatedin the line of extension of an electrode of the other group in fact, theelectrode 36 is in the line of extension of the electrode 44, theelectrode 38 is in the line of extension of the electrode 46 and soforth. In order to ensure that the distribution of potential should bestrictly that of a quadrupole lens, the electrodes 34 have the shape ofa quadric of revolution. As a first approximation and as shown in FIG.1, said electrodes can be cylinders of revolution, the free ends thereofbeing half-spheres having the same radius. The parallel plates 20, 22and 24 are maintained in rigidly fixed relation by suitable means suchas a rod 52 and two spacer members 54 and 56. Means which are. not shownin the single figure serve to polarize the electrodes 34. By way ofexample, said means can be partly constituted by a printed circuitformed of a film layer of electrically insulating material deposited onthose faces of the plates 22 and 24 which are located opposite to theelectrodes 34 and of a metallic film which is selectively deposited onsaid electrically insulating film layer.

All the electrodes 34 are brought to the same electric voltage atabsolute value, said voltage being measured with respect to a referencepotential which is the last stage of the ion source, said source beingplaced at the entrance of the micro-lens system. Moreover, thepotentials of the electrodes 34 are of opposite sign when these latterare on the one hand adjacent to and on the other hand in the line ofextension of each other by way of example, the electrodes 36, 42, 46 and48 are brought to a potential V while the electrodes 38, 40, 44 and 50are at a potential V.

This device operates in the same manner as the first embodiment whichhas already been described. A parallel ion beam of substantial width asshown by the arrows 58 arrives perpendicularly to the plate whichconstitutes the entrance of the micro-lens system. By passing throughthe bores 26, said wide beam is split up into a plurality of smallparallel beams having small cross-sectional areas. Each of said smallbeams is reduced to a micro-beam which traverses the plate 22 through asmall bore 30, is initially focused by a first group of four electrodesof a micro-lens and then focused a second time by the second group offour electrodes of said micro-lens. The micro-beams which pass throughthe bores 32 of the plate 24 are accordingly convergent. The focallength of the micro-lenses depends on the one hand on the energy of theincident ions and on the other hand on the electric voltage which isapplied to the electrodes 34. By modifying the voltage of saidelectrodes, it is possible to vary the focal length in consequence, at apredetermined distance from the exit of the micro-lens system, it ispossible to vary the dimensions of the zones in which the microbeamsimpinge on a target. When it is desired to maintain the focal points ofthe micro-lenses in the same plane, it is only necessary to vary theelectrical voltages applied to the electrodes 34 in proportion to theenergies of the incident ions (in other words, the electric voltages tobe applied to the electrodes vary in the same proportion as the energyof the ions).

The plates 20, 22 and 24 can advantageously be fabricated from aluminawhich has excellent mechanical strength and permits of machining to veryaccurate dimensions. The electrodes 34 can also be formed of alumina andin this case a metallic film is deposited on the surface of eachelectrode 34.

By way of example, the dimensions of the device which is illustrated inFIG. 4 can be the following length of electrodes 6 to 8 mm distancebetween oppositely-facing electrodes 8 mm diameter of bores 26 1 mmdiameter of bores 30 and 32 0.2 mm ;diameter offiliform electrodes 1 mmdistance between the axes of two adjacent electrodes 2 mm. This deviceretains the advantage of the first embodiment while being 'more simplein mechanical design, thereby facilitating the alignment of theelectrodes. Moreover, the distribution of the lines of electric forcewithin the micro-lenses is improved and this has the effect ofreducingthe dimensions of focal spots.

The embodiments which are illustrated in FIGS. 1 and 4 can be mounted ina rigid and permanent manner by fixing the plates 2, 3 and 4 or 20, 22and 24 within a sleeve formed of electrically insulating material suchas alumina, for example. Another mode of procedure consists in fixingthe plates 2 and 3 or 20 and 22 and in mounting the plate 4 or 24 on asupport which is capable on the one hand of undergoing a movement oftranslation in two directions at right angles to each other and on theother hand of undergoing a movement of rotation. These movements canadvantageously be carried out by means of stepping motors. The advantageof the design solution which has just been mentioned lies in thepossibility of obtaining excellent centering of the electrodes withrespect to the different bores of the device and therefore of obtainingmaximum intensity of the micro-beams as well as perfect focusing.

By way of example of industrial application, mention can be made of adevice which is similar to that hereinabove described and illustrated inFIG. 1 or FIG. 4 and which has been employed in the collective formationof integrated micro-circuits by the method of ion implantation. It hasthus been possible to fabricate l,000 or 2,000 identical integratedelectric circuits both simultaneously and in a relatively short periodof time. The use ofa device in accordance with the invention and incombination with other devices is described in copending U.S.Application Ser. No. 107,354, filed Jan. 18, 1971, by Philippe Glotin etal., for Method and Device for Obtaining Parallel and Focused IonicMicro-Beams and Application of Said Method To The Collective Formationof Electric Circuits By Ion Implantation."

Moreover, the invention can be employed for obtaining a plurality ofelectron micro-beams which are capable of carrying out collectively alarge number of operations such as machining, welding, cutting ofthinfilm resistors and capacitors, irradiation of sensitive resins,cutting of screens and the like.

What we claim is 1. Apparatus for transforming a beam of chargedparticles of large cross-section into a plurality of microbeams ofparticles which micro-beams are substantially parallel and focusedcomprising a ring of filiform electrodes substantially parallel to theaxis of the beam of particles of large cross-section, two plane spacedplates supporting said electrodes at the vertexes of a square, aplurality of openings in said plates dividing the beam, said openingsbeing disposed at the verticies ofa square similar to the first square,four adjacent ones of said electrodes being symmetrically disposedaround the axis of each of said openings, electric means for applyingelectric potential to said electrodes whereby the space between fouradjacent ones of said electrodes has a quadrupolar electrostatic field,a group of said four electrodes forming an quadrupolar electrostaticmicrolens.

2. A system of electrostatic quadrupole micro-lenses as defined in claim1, including .spaced flat plates supporting said electrodes and thediameter of said bores of one of said plates being very substantiallysmaller than the diameter of the bores of the other of said plates.

3. A system of electrostatic quadrupole micro-lenses as defined in claim1, wherein said electrodes are wires of electrically insulatingmaterial, each of said electrically conducting portions being a metallicfilm which is deposited on said wires.

4. A system of electrostatic quadrupole micro-lenses as defined in claim1, wherein said plates are each provided with a printed circuitconstituted by a film of electrically insulating material covering thatface of said plates which is located nearest said electrodes and anelectrically conducting film which is deposited selectively on saidinsulating material, the function of said circuit being to polarize saidelectrodes.

5. A system of electrostatic quadrupole micro-lenses as defined in claim1, wherein said plates are fixed within a sleeve formed of insulatingmaterial.

6. A system of electrostatic quadrupole micro-lenses as defined in claim1, wherein one plate is stationary and the otherplate is rigidly fixedto a support which is capable of carrying out two movements oftranslation in two directions at right angles to each other and amovement of rotation.

7. Apparatus as described in claim 1, each of said quadrupolarmicro-lenses being formed of two groups of electrodes, each of saidgroups being formed by four adjacent ones of said electrodes, each ofsaid electrodes of one of said two groups being located in the line ofextension of an electrode of the other of said groups.

8. A system of electrostatic quadrupole micro-lenses as defined in claim7, wherein each electrode has the shape of a quadric.

9. A system of electrostatic quadrupole micro-lenses as defined in claim7, wherein each electrode is a cylinder of revolution terminating in ahalf-sphere having the same radius.

10. A system of electrostatic quadrupole micro-lensees as defined inclaim 7, wherein each electrode is constituted by a cylindrical rodwhich is formed of insulating material and the entire surface of whichis coated with an electrically conducting layer.

11. Apparatus as described in claim 1, the diameter of said openingsbeing substantially smaller than the spacing between two of saidadjacent electrodes.

1. Apparatus for transforming a beam of charged particles of largecross-section into a plurality of micro-beams of particles whichmicro-beams are substantially parallel and focused comprising a ring offiliform electrodes substantially parallel to the axis of the beam ofparticles of large cross-section, two plane spaced plates supportingsaid electrodes at the vertexes of a square, a plurality of openings insaid plates dividing the beam, said openings being disposed at theverticies of a square similar to the first square, four adjacent ones ofsaid electrodes being symmetrically disposed around the axis of each ofsaid openings, electric means for applying electric potential to saidelectrodes whereby the space between four adjacent ones of saidelectrodes has a quadrupolar electrostatic field, a group of said fourelectrodes forming an quadrupolar electrostatic micro-lens.
 1. Apparatusfor transforming a beam of charged particles of large cross-section intoa plurality of micro-beams of particles which micro-beams aresubstantially parallel and focused comprising a ring of filiformelectrodes substantially parallel to the axis of the beam of particlesof large cross-section, two plane spaced plates supporting saidelectrodes at the vertexes of a square, a plurality of openings in saidplates dividing the beam, said openings being disposed at the verticiesof a square similar to the first square, four adjacent ones of saidelectrodes being symmetrically disposed around the axis of each of saidopenings, electric means for applying electric potential to saidelectrodes whereby the space between four adjacent ones of saidelectrodes has a quadrupolar electrostatic field, a group of said fourelectrodes forming an quadrupolar electrostatic micro-lens.
 2. A systemof electrostatic quadrupole micro-lenses as defined in claim 1,including spaced flat plates supporting said electrodes and the diameterof said bores of one of said plates being very substantially smallerthan the diameter of the bores of the other of said plates.
 3. A systemof electrostatic quadrupole micro-lenses as defined in claim 1, whereinsaid electrodes are wires of electrically insulating material, each ofsaid electrically conducting portions being a metallic film which isdeposited on said wires.
 4. A system of electrostatic quadrupolemicro-lenses as defined in claim 1, wherein said plates are eachprovided with a printed circuit constituted by a film of electricallyinsulating material covering that face of said plates which is locatednearest said electrodes and an electrically conducting film which isdeposited selectively on said insulating material, the function of saidcircuit being to polarize said electrodes.
 5. A system of electrostaticquadrupole micro-lenses as defined in claim 1, wherein said plates arefixed within a sleeve formed of insulating material.
 6. A system ofelectrostatic quadrupole micro-lenses as defined in claim 1, wherein oneplate is stationary and the other plate is rigidly fixed to a supportwhich is capable of carrying out two movements of translation in twodirections at right angles to each other and a movement of rotation. 7.Apparatus as described in claim 1, each of said quadrupolar micro-lensesbeing formed of two groups of electrodes, each of said groups beingformed by four adjacent ones of said electrodes, each of said electrodesof one of said two groups being located in the line of extension of anelectrode of the other of said groups.
 8. A system of electrostaticquadrupole micro-lenses as defined in claim 7, wherein each electrodehas the shape of a quadric.
 9. A system of electrostatic quadrupolemicro-lenses as defined in claim 7, wherein each electrode is a cylinderof revolution terminating in a half-sphere having the same radius.
 10. Asystem of electrostatic quadrupole micro-lenses as defined in claim 7,wherein each electrode is constituted by a cylindrical rod which isformed of insulating material and the entire surface of which is coatedwith an electrically conducting layer.